GIS in the General Management Plan

ABSTRACT:
GIS was used on a variety of occasions to help convey information and make management decisions in the development of Saratoga National Historical Park's General Management Plan, currently on policy review in Washington, D.C. The purpose of the GMP is to specify a clearly defined direction for resource preservation and visitor use in the park for the next 20 years. It is intended to serve as a planning tool for park managers and to provide information on the park’s management direction to the public.

Three notable examples of the use of GIS in the GMP were the creation of a three-dimensional park map, a series of “battle narrative” maps, and an analysis of the landscape treatment proposed for each GMP alternative. All work was done “in-house” by the Boston Support Office’s Planning and Legislation Group (authors of the GMP) on desktop ArcView 3.2a, with assistance from the park and the University of Rhode Island's Environmental Data Center.

BACKGROUND:
Saratoga National Historical Park’s battlefield preserves the site of the Revolutionary War battles of Saratoga that occurred along the western bank of the Hudson River during the autumn of 1777. The park’s battlefield unit is located in upstate New York, eight miles south of Schuylerville and is currently composed of 3,305 NPS owned acres. In 1777 - the second year of America’s War for Independence - the British sought to quell the rebellion with a single decisive military campaign. Their plan depended on using an invading army to divide the colonies along a natural corridor of rivers and lakes stretching from Canada to New York City. The American commitment to halt this invasion at Saratoga proved critical to the future of an emerging nation.

The physical geography of the upper Hudson was a major factor in the area’s selection as a defensive position by the Americans. Not only did the site possess a natural defile which would constrict British movement south along the riverbank but the area was still heavily forested by virgin timber. Although there had been extensive clearing along the river’s floodplain there were only scattered farm clearings above the escarpment to the west. The British forces were forced to choose between a frontal assault between hills and the river or attempt to flank the American position by moving through heavily forested uplands. The British attempted the flanking maneuver and failed.

GIS TASK 1: PARK MAP
The need was identified for a general-purpose map that would display major park features and help explain the park’s dramatic landscape to the public. It would be more useful and accurate than any previous map by making use of recent orthophotography and GIS to display the varied topography and the mosaic of fields and forests.

One of the first data-gathering tasks completed in support of the GMP was the creation of true color orthophoto imagery of the entire park. To create the three-dimensional park map, the original orthos were first reduced in resolution from 0.5 meter to 3 meter. This action essentially allowed the ortho data to load faster at a reasonable resolution. The shapefiles for the park’s boundaries and roads were then included. Using 3D Analyst the data was then assigned base heights from the TIN “battle”, created from the park’s 3-meter contour dataset. The resulting image showed the high quality, true color detail of the orthoimagery and the dramatic topography of the area.. A desirable vantage point, light source, and vertical exaggeration were established. Prominent features and park boundaries were labeled. An NPS-standard title block was inserted to complete the map.

GIS TASK 2: BATTLE NARRATIVE MAPS
In order to improve visitor understanding of the events that led to the 1777 British surrender in Saratoga, the need was identified for a series of maps that showed troop positions and movements during the battles and siege of 1777 in relation to the current park boundary and features. Again, since topography and field-forest configuration played important roles in the battles, it was important to include these elements on the maps.

Illustrative battle maps, depicting troop movements and troop positions during the 1777 battles, were developed by the Olmsted Center for Landscape Preservation (OCLP) based on historical research, including field accounts and historic maps. These maps were then “rubbersheeted” into the GIS using prominent, relatively unaltered landscape features such as the Hudson River and the Great Ravine. The historic fields and forests, roads, troop movements and other features were then traced from the OCLP battle maps as new shapefiles. Using 3D Analyst, a TIN was created of the digital contour information and a shading used to describe elevational differences. The historic fields and forests, roads, troop movements and other features as well as the current park boundary were displayed with the TIN. Prominent features and park boundaries were labeled. An NPS-standard title block was inserted to complete the maps.

GIS TASK 3: LANDSCAPE REHABILITATION ANALYSIS
In the years prior to park establishment, agricultural expansion in the vicinity change much of the land cover that attributed to the outcome of the battles at Saratoga. Less than ten percent of the original forest cover present at the time of the battle remained. Therefore, managers have sought to rehabilitate key landscape features and establish viewsheds to help the visitor understand the conditions faced by the armed forces and how landscape conditions were manipulated to serve tactical needs. A major decision point in the GMP alternatives is the extent to which the park recreate the configuration of field and forest that was present at the time of the battles and whether the clearing and maintenance of certain viewsheds (areas of clearing that provide the visitor with views from a particular vantage point to a feature) should take precedence over historic land cover. A GIS analysis was completed that compared the four alternatives, which prescribe levels and areas of field-forest conversion and viewshed maintenance.

To begin the analysis, a current (2000) field-forest configuration shapefile was created by tracing the information from the orthophotos, with two landscape types: field and forest. The previous work conducted for Task 2 had generated a historic (1777) field-forest configuration, based on the rubbersheeted OCLP battle maps, and had three landscape types: field, thinned forest and forest. The third shapefile used was the viewsheds proposed in each alternative. For each alternative, the areas to reflect the historic (1777) field-forest configurations and desired viewsheds were compared with the current (2000) field-forest configurations. Thus it could be determined for each alternative five possible treatments of landscape: convert field to thinned forest or forest, convert forest to thinned forest or field, or have no change. An additional parameter was added when the park decided that these landscape treatments should only pertain to areas within the Battle Action and Encampment Zone, as part of the GMP zoning. A map for each of the four alternatives and acreage calculations for each treatment were created.